Page:Popular Science Monthly Volume 82.djvu/246

242 instead of forming in larger proportion as the temperature is raised, it forms in smaller proportion; thus, if a mixture of nitrogen and hydrogen be heated for a long time to 800° centigrade, only one hundredth of one per cent, of ammonia forms, while it can be calculated that at 400° one half of one per cent, of ammonia must finally result. We ought therefore to work at as low a temperature as possible; but we then meet the difficulty that the rate of combination becomes extremely slow. Thus, owing to the extreme inertness of nitrogen, no detectable quantity of ammonia is produced, even when nitrogen and hydrogen are heated together for several hours at 400°. When, however, it is known that a chemical change tends to take place in a certain direction and when the only difficulty is that it is going on too slowly, there is always a reasonable hope of overcoming this difficulty; for we know that chemical changes are often greatly accelerated by mere contact with suitable solid substances. Such substances are called catalyzers, and Professor Wilhelm Ostwald, one of Germany's distinguished scientists, predicted a dozen years ago that the great advances in the chemical industries within the next few decades would be made through the more extensive employment of catalytic processes. This prediction has found one of its many fulfilments in the commercial development of the method for the production of ammonia here under consideration. For after many years' investigation, certain metals have been found which cause a rapid combination of nitrogen and hydrogen even at comparatively low temperatures. The first metal that was found to have this power in a marked degree was osmium, a metal similar to platinum. As the total quantity of this element in our possession is estimated to be 200 pounds, and as it is valued at about $1,000 a pound, this discovery was hardly a practical one. Later it was found, however, that under special conditions some of the commoner metals, such as uranium, manganese, and even iron, when extremely pure, can be made to serve the purpose. Without entering into further details, it may be stated that a satisfactory yield of ammonia can be attained by carefully purifying the hydrogen and nitrogen gases, by highly compressing them (up to 50 or 100 atmospheres) and then passing the compressed gases slowly over one of these metals at 500-600°; and that a large factory for the manufacture of ammonia by this process is now being erected in Germany.

Certain other chemical processes for the fixation of atmospheric nitrogen, less direct than those already described, but nevertheless commercially practicable, have also been developed and put into operation within the past ten years. There is therefore little doubt that from these sources a large additional supply of nitrogen-compounds will soon be available and that their cost will be gradually lowered. To the vital problem of feeding the human race the chemist is therefore making an important contribution.